## Argonne’s “Omnivorous Engine”; Baselining Gasoline, Ethanol and Butanol

##### 21 July 2008
 The test engine is based on an Opel 2.2L Ecotec Direct engine. Click to enlarge.

Among the projects of Argonne National Laboratory’s Transportation Technology R&D Center is the development of the “omnivorous engine”. The project seeks to combine in-cylinder measurement technology and advanced controls to optimize spark timing, the quantity, and the timing of injected fuel to produce an engine that will be able to run on any liquid spark ignition fuel with optimal efficiency and low emissions.

Argonne is using in-cylinder ionization sensing to provide real-time analysis of fuel burn rates. This combustion signature analysis ability enables detection of the kind of fuel used to determine optimal spark timing. In addition, this information enables control of other engine parameters, such as boost to increase effective compression ratio and exhaust gas recirculation rates to control exhaust emissions.

Argonne is initially baselining gasoline and ethanol at stoichiometric air/fuel ratios, and has begun expanding to other renewable fuels such as butanol. In April, the researchers presented a paper comparing gasoline and gasoline/ethanol blend combustion at the SAE World Congress in April, and a paper comparing ethanol and butanol as oxygenates at the ASME Internal Combustion Engine Division 2008 Spring Technical Conference.

The basic engine for all tests was a spark-ignited, direct injection Opel 2.2L Ecotec Engine (GM L850) with the cylinder head modified for cylinder pressure transducers. The stock engine operates with a compression ratio of 12:1 and delivers 114 kW of power @ 5600 rpm and maximum torque of 220 Nm @5600 rpm.

The engine control unit (ECU) controls engine operation parameters based on sensor inputs as well as driver demand. The sensors available on this particular engine setup are:

• Crank angle position
• Camshaft position
• Fuel rail pressure
• Engine coolant temperature
• Knock
• Throttle position feedback
• Exhaust oxygen content before catalyst
• Exhaust oxygen content post catalyst
• EGR valve position
• Swirl valve position
• Intake air mass air flow

The ECU calculates engine operational setting based on input from the sensors and driver demand using equations and look-up tables. The main output functions of the ECU are:

• Fuel injection timing
• Fuel injection duration
• Fuel injection pressure
• Ignition timing
• Exhaust gas recirculation (EGR) rate
• Swirl plate position

In the SAE paper, the Argonne team used the stock calibration of the injection parameters (fuel pressure and injection timing), nor were the position of the swirl control valve or the EGR rate changed when the engine was operated on the different ethanol/gasoline blends. The intent of the first study was to assess the effects on combustion behavior, efficiency, emissions, and performance of various blends of gasoline and ethanol without any adjustment of calibration parameters, on an engine calibrated for gasoline.

Fuels tested against a baseline fuel of pure gasoline were blend ratios of 10% (E10), 20% (E20), 50% (E50), and 85% (E85).

 Comparison of brake thermal efficiency. Click to enlarge.

Results from this work showed that in a wide range of low- and medium-load operation,  neat gasoline and blends of ethanol and gasoline (E10, E20, E50 and E85) show very similar results in terms of brake thermal efficiency, with only high engine loads and blends with high ethanol content showing significant advantages in brake thermal efficiency. Other findings from this study included:

• The combustion behavior expressed as combustion speed, combustion stability, rates of heat release and combustion phasing do not show significant differences among the different blends of fuel.

• Blends with higher ethanol content do show advantages in terms of regulated emissions, both for oxides of nitrogen (NOx) as well as total hydrocarbons (THC). These advantages are mainly due to the fuel composition such as lower aromatic content as well as the higher latent heat of vaporization.

The testing confirmed that:

The fact that ethanol allows for a more optimal combustion phasing at high engine loads indicates the necessity to design and calibrate an engine specifically for ethanol operation. This would permit taking full advantage of the promising combustion properties of ethanol and compensate for the lower volumetric energy content of ethanol compared to gasoline.

The ethanol-butanol study reported in the ASME paper analyzed the combustion, efficiency and emissions of pure gasoline, 10% ethanol (E10) and 10% butanol (Bu10) blends in the 2.2L engine. Major findings of this study include:

• The brake thermal efficiency was very similar between the three fuels and the peak values differed by less than 2% relative.

• Combustion analysis showed that before the onset of knock (load less than 75 Nm), the locations of start-of-combustion and peak pressure were identical for the three fuels. The magnitude of peak pressure was the highest for the Bu10 blend, the 50% MFB point was the most advanced and the maximum rate of pressure rise was highest for the Bu10 blend. This suggests the burning velocity of the Bu10 blend was higher than both the E10 blend and gasoline.

• The E10 blend had the highest octane rating which allowed the spark timing to be advanced up to five degrees compared to gasoline at the highest load of 150 Nm. At high loads, the ECU retarded the ignition timing to prevent knock with pure gasoline and the Bu10 blend, due to the lower octane rating compared to ethanol. Once knock occurs, the magnitude of peak pressure drops measurably for the Bu10 blend and the peak occurs several degrees later than gasoline or E10.

• Brake specific volumetric fuel consumption, a normalized measure of engine fuel consumption, showed an increase of approximately 3.4% for Bu10 and 4.2% for E10 compared to gasoline. Gasoline had the lowest BSVFC of the three fuels (311 ml/kWh) due to the high energy density.

• Combustion stability did not vary significantly between the three fuels, over the tested speed and load range. COV of IMEP was less than 3% for the entire operating range.

• Specific carbon monoxide emissions did not show a significant difference between gasoline and the two fuel blends. This was not an unexpected result due to the closed-loop feedback on the engine, to maintain stoichiometric operation.

• Specific THC emissions did not show significant differences between the three fuels, due to the formation and oxidation mechanisms not being dramatically altered for the three fuels. It is expected that as alcohol blend ratio increases, the impact on THC emissions should be positive due to the reduction in aromatic content in the blended fuel.

• Specific NOx emissions reflected the ignition timing changes due to knock. The E10 blend produced the highest specific NOx emissions and largest peak NOx island, due to the advanced ignition timing. The lowest specific NOx emissions were for Bu10, which had the largest ignition delay at the high load conditions due to the low octane rating of pure butanol.

The data suggests that 10 Vol-% butanol can be substituted for ethanol as an effective oxygenate, with an improvement in fuel economy and no degradation in emission or combustion stability.

Resources

• Thomas Wallner and Scott A. Miers (2008) Combustion Behavior of Gasoline and Gasoline/Ethanol Blends in a Modern Direct-Injection 4-Cylinder Engine (SAE 2008-01-0077)

• Thomas Wallner, Scott A. Miers and Steve McConnell (2008) A Comparison of Ethanol and Butanol as Oxygenates Using a Direct-Injection, Spark-Ignition (DISI) Engine (ICES 2008-1690)

It is now time to realize that electronic engine valves are now very easy to make and to operate. With such, the compression ratio can be altered at will. Air hybrids can be built as well with very little addition of weight. There is also less friction in the engine. Highly touted, and almost completely missunderstood, super capacitors can be used if momentary high power is needed for opening valves.

It would also be good to consider water as an oxygenate.

Series hybrid cars have the most flexibility of operation, and the engines for such do not need a wide operating range, and the range is even smaller if combined into a Plug-In-Hybrid. ..HG..

Cylinder head modified for transducer installation - I wonder If that is a new location for the familiar old Knock sensor? or some new device.
Citroen diesel vehicles are sold as multifueled, I'm not sure weather this means they can adapt to the fuel/quality on board but this is certainly the intention.
This system if successful will monitor and determine the best parameters for combustion, with fast processors able to monitor the engine 150 revs per second at say 1 Megahertz or ~700 samples per second.
This is so much more than adequate to fully process every firing on the fly, when combined with the adaptive strategy and map we should expect a very efficient use of a wide range of fuels.
This is the flip side to the tight control and regulation (expensive and inefficient) of the wide variety of fuels with associated cross contamination, let alone availability and large numbers of dedicated fuel storage tanks. ( A recipe for disaster)
Of course if you don't have this capability, then one should expect a conflict ,if not a torment.

I suspect this research is a combination of advanced sensors that will become affordable in the near future and advanced sensors that are not expected to become practical soon. This way they pioneer the use of new sensors and obtain valuable data on actual operation and, in so doing, determine which new sensors are most cost effective.
Good basic research; probably much like what GM, Ford, Toyota, Honda, etc. have done, maybe years ago, but the results were kept secret.
It is a disappointing that over a wide range, gasoline and blends of ethanol and gasoline (E10, E20, E50 and E85) show very similar efficiency results, but that’s why it takes some basic research to root out where engine modifications and fuel blends can provide advantages.
Most knock sensors are not intrusive and simply “listen” for the knock peculiar to detonation.
I think the power switching and the cost, weight and durability of the solenoids, not the sudden power drain, are the drawbacks with electronic engine valves.
I am not sure this effort is to develop an engine that can adjust widely to a widely different fuels, but to determine what makes an engine most flexible and which fuels make this most practical. 200 million engines with high \$ sensors makes no sense. If this were the required, just put different dyes in the different fuel types and a color sensor in each engine.
Also note that, so far “a wide range of low- and medium-load operation, neat gasoline and blends of ethanol and gasoline (E10, E20, E50 and E85) show very similar results in terms of brake thermal efficiency”.

Electric motors run on any electricity.

Not quite, some require A.C. others D.C.

I wonder: what is the point of having an engine that can run on mixtures of different fuels. Is it less expensive to make Ethanol and Butanol than to make Alkanes by the Fischer-Tropsch process.

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